One of the week's biggest news stories is the shooting death of black Florida teenager Trayvon Martin, and the inability or unwillingness of the local police to charge his killer, George Zimmerman. On Friday morning, President Obama weighed in heavily, urging national "soul searching" to better understand how this tragedy occurred. Then Obama got personal: "When I think about this boy, I think about my own kids. ... If I had a son, he'd look like Trayvon." Obama's GOP counterparts have been somewhat less open. Until Newt Gingrich spoke out on Thursday night, telling CNN's Piers Morgan that Martin's death is a "tragedy," the GOP presidential field has been conspicuously silent on the issue, and likely nominee Mitt Romney had even ignored reporters' questions about Martin's shooting. "Why have they been so noticeably silent... about the shooting of an innocent 17-year-old black boy?" says Lawrence D. Elliott in Technorati. Here, five theories: 

1. They fear upsetting Florida's influential Republicans
Martin's killing became national news the same week that Romney all but locked up the GOP nomination, aided by a coveted endorsement from former Florida Gov. Jeb Bush (R). Another influential Floridian, Sen. Marco Rubio (R), is among Romney's top VP picks. Both Bush and Rubio strongly backed the expansive gun law that has kept Zimmerman out of jail. If Romney wants to stay allied with them, says Kelly Virella at Dominion of New York, he'd have to stake out "a pro-'Shoot First,' pro-Zimmerman stance" that's out of step with popular opinion. It's easier, and safer, to say nothing.

2. Romney doesn't want to offend the NRA
Any comments that paint Martin's killing in a negative light would also sit poorly with another important GOP constituency: The deep-pocketed gun lobby, says Dominion of New York's Virella. Romney has a cordial but not warm relationship with the National Rifle Association (NRA), which was a major driving force behind Florida's controversial gun law. In this expensive campaign, no Republican wants to risk losing "campaign contributions from the NRA."

3. Addressing the killing has no political upside
Who would cheer Romney or Santorum for condemning the killing? asks Frank Rich at New York. The GOP "has very few African-American adherents and is prone to claiming that all cases like this are hoaxes trumped up by liberals." On top of that, every Republican is courting the Latino vote, and Zimmerman is half Latino. 

4. Republicans have forgotten their roots
The silence on what appears to be a racially motivated killing is pure political cowardice, says Michelle D. Bernard at The Hill. The Party of Lincoln "was birthed in the moral crusade to abolish slavery," and it would be nice to know that today's Republicans "running for the highest office of the land will not remain silent when our young black men are killed."

5. Nobody wants to politicize a local crime
Romney and Santorum probably aren't eager to wade into the Martin case for some of the same reasons Obama waited so long to speak up, says Earl Ofari Hutchinson in Electronic Urban Report. As the president learned from the "instant and rabid" reaction to "his mild rebuke of the white officer that cuffed Harvard professor Henry Louis Gates in 2009," it's sometimes counterproductive for national political leaders to opine about local law enforcement matters, especially when race is involved.